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Percorrer por autor "Macek, Wojciech"

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  • Quasistatic and fatigue behavior of an AISI H13 steel obtained by additive manufacturing and conventional method
    Publication . Garcias, José F.; Martins, Rui F.; Branco, Ricardo; Marciniak, Zbigniew; Macek, Wojciech; Pereira, Cândida; Santos, Cyril
    This work aims to compare the mechanical behavior of an AISI H13 steel obtained by additive manufacturing with that obtained by conventional manufacturing methods. The average values of the ultimate tensile strength (UTS) and ductility obtained for the specimens produced by the conventional method were equal to 658 MPa and 18%, respectively, which compares with 503 MPa and 0.75% registered for the selective laser melting (SLM) specimens. Inversely, the average hardness value determined for the SLM specimens was higher, 450 HV, than the observed for the conventional, 200 HV. In addition, the maximum applied stress corresponding to a fatigue limit's endurance of 2 × 106 cycles was equal to 340 and 85 MPa for conventional and SLM specimens, respectively. Therefore, from a fatigue design point of view, it was possible to infer that σmax/UTS = 0.17 for the SLM specimens tested. Porosity and lack of fusion influenced the static and the fatigue strength negatively in the SLM specimens.
    2021-08-19Artigo científico Acesso aberto Ver mais
  • Strain sequence effect on fatigue life and fracture surface topography of 7075-T651 aluminium alloy
    Publication . Macek, Wojciech; Branco, Ricardo; Costa, José Domingos; Pereira, Cândida
    The paper studies the effect of strain-loading sequence on fatigue lifetime and fracture surface topographies in 7075-T651 aluminum alloy specimens. Fatigue tests were performed in two ways: (i) constant-amplitude loading and (ii) two series of variable amplitude loading with non-zero mean strain values. The topography of the fatigue fractures was measured over their entire surfaces with the help of an optical confocal measurement system. The results of fatigue tests in the form of equivalent strains, εaeq, such as the weighted mean of strain components, εa1, εa2, and fatigue life, Nf, were used as the sum of the partial number of cycles N1, and N2. This study indicates, inter alia, that the values of the fracture surface parameter core height Sk, found in the two-step loading program, are linearly dependent on the equivalent strain, and logarithmically dependent on the fatigue life.
    2021-09Artigo científico Acesso aberto Ver mais